An object to be machined can be machined by converging a laser beam outputted from a laser light source through a converging optical system and irradiating the object with thus converged laser beam. The object can be machined into a desirable form by scanning a laser beam at a single converging position if the laser beam is converged by using a lens alone. However, it takes a long time for machining in this case.
The easiest technique for reducing the machining time is performing multipoint simultaneous machining by emitting converged laser beams at a plurality of converging positions. The multipoint simultaneous machining can be carried out by using a plurality of laser light sources and converging the respective laser beams outputted from the laser light sources through lenses, for example. In this case, however, the use of a plurality of laser light sources increases their cost and complicates their installation area and optical systems.
An invention aimed at solving such a problem is disclosed in Patent Literature 1. The invention disclosed in Patent Literature 1 causes a phase-modulating spatial light modulator to display a hologram, so as to phase-modulate a laser beam outputted from a single laser light source, and irradiates a plurality of positions simultaneously with thus phase-modulated laser beam converged through a converging optical system. The hologram displayed in the spatial light modulator has such a phase modulation distribution as to converge the laser beam at a plurality of converging positions through the converging optical system.    Patent Literature 1: Japanese Patent Publication No. 2723798